Molecular targeting of proteins by L-homocysteine: mechanistic implications for vascular disease

Area of Science:

• Biochemistry
• Pathophysiology
• Molecular Biology

Background:

• Hyperhomocysteinemia is a known risk factor for cardiovascular disease, pregnancy complications, cognitive decline, and osteoporosis.
• Vascular dysfunction due to elevated homocysteine is hypothesized as a common link between these diverse pathologies.
• The precise molecular mechanisms underlying homocysteine's cytotoxicity and role in atherogenesis remain incompletely understood.

Purpose of the Study:

• To elucidate the chemical properties of homocysteine that contribute to its cytotoxicity.
• To explain the pathogenic mechanisms linking elevated homocysteine to various diseases.
• To identify specific protein targets of homocysteine modification.

Main Methods:

• Focus on the unique chemistry of the homocysteine molecule.
• Investigate the role of the sulfhydryl group's high pKa (10.0) in protein interactions.
• Identify and characterize protein targets of homocysteinylation through laboratory studies.

Main Results:

• Homocysteine's high pKa facilitates stable disulfide bond formation with protein cysteine residues, leading to functional impairment.
• Identified albumin, fibronectin, transthyretin, and metallothionein as direct targets of homocysteinylation.
• Demonstrated that homocysteinylation of fibronectin impairs fibrin binding and metallothionein disrupts zinc binding and superoxide dismutase activity.

Conclusions:

• S-homocysteinylation of protein cysteine residues provides a mechanistic explanation for the observed cytotoxicity of elevated L-homocysteine.
• Understanding these molecular interactions is crucial for developing targeted therapies for homocysteine-related pathologies.
• This review highlights the critical role of protein modification by homocysteine in diverse disease states.